In communication systems and computer systems, a so called prioritization function resolves conflicts in situations where resources in the systems are limited. The conflicts relate to which task or connection should be allowed to use the resources.
A known method for prioritization is based on pre-emption. In a pre-emption based prioritization method for a computer system, an ongoing task will be interrupted for the benefit of a further task with higher priority than the ongoing task. When the ongoing task is interrupted, its resources are released and thus returned to the system before the ongoing task has been completed, i.e. the ongoing task is pre-emptied. Then the returned resources may be used by the further task. It is intended that the interrupted task, which previously was the ongoing task, will be resumed when the further task with higher priority has been completed. Queuing schemes place tasks in a queue, in which the tasks remain while waiting for resources to be available. In the context of a computer system, a resource is released when the further task is finalized.
In cellular radio communication systems, prioritization is performed at many levels. For example, prioritization for a connection associated with a user equipment is managed at a level where admission control occurs. The admission control for the connection is performed by a radio base station of the cellular radio communication system at initial access and at handover of the user equipment. Hence, when a user equipment needs a connection, a request is sent from the user equipment to the radio base station which then controls admission of the request.
During handover, a connection of the user equipment may be moved from a first base station to a second base station. Hence, an aspect of mobility applies to connections, but not to tasks. In cases when the second base station is at congestion, i.e. resources available for connections are sparse or non-existent, the second base station priorities resources to be used for handling user equipments performing handover to the second base station. When user equipments performing handover are prioritized, it may happen that a user equipment performing initial access to the second base station is not allowed to access the second base station. In this manner, mobility of user equipments is provided as seamlessly as possible.
When dealing with congestion, a key aspect is how inactive User Equipments (UE) are managed in the base station. In typical radio interfaces, such as International Mobile Telecommunication 2000 (IMT-200) family and its enhancements, resource allocations are strongly influenced by a protocol state model. The protocol state model defines two states of a user equipment in relation to a base station; connected state and idle state. Radio resources are allocated to user equipments in connected state. The radio resources are released when the user equipment is transitioned to idle state. The transition from connected state to idle state is usually performed when the user equipment has been inactive for a specific time period, which will be referred to as an idle state time period herein. When the idle state time period has passed, it is no longer plausible to assume that the user equipment will send or receive any user data in a near future.
According to a known method for prioritizing handover over initial access a reservoir of radio resources are reserved. The reservoir of radio resources are reserved for the benefit of admitting a request for radio resources in conjunction with handover (handover request) to the base station. Should the base station be completely congested, i.e. the only radio resources available for allocation are those in the reservoir, any request for radio resources in conjunction with initial access (initial access request) will be blocked. In effect, the number of connections typically held by the base station is reduced, since the reservoir will always reserve some radio resource for handover requests. Though, sometimes all reserved radio resources may be allocated to connections established in response to handover requests.
In Long-Term Evolution (LTE) systems, prioritization at the level of admission control is suggested to be handled by an Allocation and Retention Priority (ARP) function. With the ARP function, different levels of priority may be set for different connections. Therefore, when a first base station detects that a first connection needs to be handed over to a second base station, the level of priority for the first connection is increased, or boosted. When a second connection at the second base station has a lower priority level than the increased level of priority of the first connection, the radio resources of the second connection will be released in case the second base station has no available radio resources. Hence, a request pertaining to radio resources for the first connection will be admitted thanks to that the radio resources of the second connection can be used by the first connection. In this manner, it is intended to be assured that the request for radio resources, to be used by the first connection, at the second base station is admitted. If a first ARP level of the first connection, before the first ARP level is increased due to on-going handover, and a second ARP level of the second connection are the same, a problem may arise. The problem is that it is not straight forward to determine which of the first and second connections to prioritize. It seems inappropriate to release the already admitted second connection, just because the first connection is performing handover. It seems inappropriate because the first and second connections are comparable in terms of priority, i.e. the connections have the same or similar ARP level(s). Moreover, considering the amount of possible ARP levels, it is expected to be cumbersome to determine which ARP level to assign to the connection in order to obtain a desired prioritization.